How long will new balls last?

How long will a sealed can of new tennis balls last?
I've heard hearsay ranging from a couple months to years on end.

I plan to order a case or two of balls, but with cold weather/winter coming, I won't use them all up, and I dont want the unused new ones to die out.

Thanks for responses!

EDIT: Also, is there any sure way of knowing when a can of balls was manufactured/pressureized in a can?
Because, for example, if I buy a can in June 2007, it doesnt mean it was made in June 2007. It could've been manufactured/pressureized in 2006, or even before, but was just sitting on the store shelf. So how would one go about being sure a can of balls is "fresh"?

I read somewhere someone said 2 years shelf life is the norm. But I heard that there can be micro leaks in the can over time. I guess it depends on how well the seal is made in the manufacturing process.

I personally have opened up Wilson Titanium cans that are 4 years old since I bought them and the balls seem OK. I have also opened up Penn cans that are between 2 to 3 years old since purchase and they seem OK, too. But I think those Penn balls could be a little firmer than they were.

I think most cans have some kind of codes stamped on them indicating their lot numbers or something like that. But you'd probably need a decoder ring from the manufacturer to translate those codes into manufacturing dates.